A wide spread availability of camera phones having a camera function in recent years has increased the opportunities for users to photograph various kinds of photographic subjects. For example, a photographic subject at a distance from the camera lens, such as a friend or scenery, is photographed (normal snapshot) or a photographic subject at a close distance from the camera lens, such as a bus time schedule or flower petals, is photographed (close-up photography).
For close-up photography (macro photography), the camera lens needs to be positioned slightly closer to the photographic subject than for a normal snap shot. Therefore, a photographing lens system of this kind is equipped with a drive mechanism that drives the lens to be displaced in the optical axis direction; by switching a switch, the drive mechanism is driven to move the lens in the optical axis direction (see Patent Reference 1, for example).
The lens driving apparatus disclosed in Patent Reference 1 comprises a movable body having lenses and a fixed body that moves the movable body in the lens optical axis direction while holding the movable body; a drive magnet is arranged to the movable body and a coil and two magnetic pieces (yokes) are arranged to the fixed body. When electrification to the coil is stopped, the magnetic adsorption between the drive magnet and the magnetic pieces is used to retain the movable body at a position of one of the above-mentioned magnetic pieces to which the movable body is closer. Therefore, this type of lens driving apparatus has a simple configuration and requires fewer components, which is suitable to downsizing.    [Patent reference 1] Japanese Unexamined Patent Application (Tokkai) NO. 2005-37865
However, the lens driving apparatus disclosed in the above mentioned Patent Reference 1 has a problem that there are only two points to determine the position of the movable body (that is, the lens position), making it difficult to determine the middle position of the lens.
In other words, as described above, the movable body holding lenses is to be retained at a position of one of the two magnetic pieces to which the movable body is closer; therefore, it is difficult to position the lenses in desired positions between the lens position for close-up photography and the lens position for a normal snapshot. If it is difficult to position the lenses in desired positions, a further improvement of the focusing function cannot be expected as a result.
For example, one sometimes takes a picture of himself (self photography) using a camera phone. That is, the distance between the camera lens and a photographic subject is not too far, compared to the photographing of friends or scenery, but not too close, either, compared to the photographing of a bus time schedule or flower petals. In this case, a conventional camera phone uses the lens position for a normal snapshot (which means that the lens position for a normal snapshot is alternatively used); however, it is still desired to position the lenses in desired positions between the lens position for a normal snapshot and the lens position for close-up photography in order to obtain a focused, crisp image.
At least an embodiment of the present invention is devised considering the above problems; at least an embodiment of the present invention provides a lens driving apparatus that can position the lenses in desired positions so that the focusing function can be improved.
At least an embodiment of the present invention presents a lens driving apparatus that comprises a movable body holding lenses, a fixed body in which the movable body is mounted movable along the lens optical axis, and a drive mechanism that moves the movable body in the lens optical axis direction; wherein the drive mechanism is equipped with a coil that is held in either the movable body or the fixed body, a magnet held in the other body, and a regulatory means that regulates the movement of the movable body which is induced by an electromagnetic force generated when current is passed through the coil.
In at least an embodiment of the present invention, the drive mechanism is equipped with a coil that is held in either the movable body or the fixed body, a magnet held in the other body, and a regulatory means that regulates the movement of the movable body which is induced by an electromagnetic force produced when current is passed through to the coil. Therefore, the movable body can be retained in the desired position.
In other words, when the current is passed through the coil under the condition in which a magnetic flux emanated from a magnet is interlinked with the coil, an electromagnetic force is produced. Then, when the coil is arranged in the movable body, an electromagnetic force itself is exerted on the movable body and the movable body starts moving in the lens optical axis direction. Also, when the coil is arranged in the fixed body, a force reactive to the electromagnetic force is exerted on the movable body and then the movable body starts moving in the lens optical axis direction. At that time, a force to prevent the movement of the movable body is produced by the above-mentioned regulatory means; when the force to move the movable body and the force to regulate the movement of the movable body attains equilibrium, the movable body is halted. Thus, the movable body can be halted in the desired position by adjusting the amount of current flowing in the coil and the force that the regulatory means exerts on the movable body.
In this manner, the lenses can be positioned in desired positions between the lens position for close-up photography and the lens position for a normal snapshot; a crisp image can be obtained even for self-photography, for example, and the focusing function of the lens driving apparatus can be improved. Also, the lens driving apparatus can be made thinner.
The “regulatory means” here is a means to produce a force in the direction opposite from the moving direction of the movable body. It is preferred that the magnitude of the force be varied depending to the moving distance of the movable body. For example, a resilient member such as a flat spring, a coil spring, a magnetic spring or a rubber may be used as the regulatory means; or the N pole (S pole) magnet is placed on the fixed body and the N pole (S pole) magnet is placed on the movable body to generate a magnetic repulsive force, which can be used as a regulatory means. Any such device can be used for the regulatory means.
Also, “when an electromagnetic force is produced” does not mean to eliminate “when an electromagnetic force is not generated”. In other words, the above mentioned “regulatory means” can regulate the movement of the movable body by using a resilient force even when current is not passed through the coil and an electromagnetic force is not generated.
In at least an embodiment of the present invention, the regulatory means can use a resilient member that urges the movable body in the lens optical axis direction. According to at least an embodiment of the present invention, a resilient member that urges the above mentioned movable body in the lens optical axis direction; therefore, the linearity between the moving distance of the movable body and the current flowing in the coil can be improved. In other words, since a resilient member such as a flat spring has an established linear relationship between the resilience (stress) and the amount of displacement, a resilient member used as the regulatory means can contribute to the improvement of the above mentioned linearity.
In at least an embodiment of the present invention, the resilient member is composed of a first resilient member and a second resilient member that are able to urge the movable body in the lens optical axis direction. According to at least an embodiment of the present invention, the above mentioned resilient member is composed of two resilient members: one urges the movable body in one direction in the lens optical axis direction; the other urges the movable body in the opposite direction in the lens optical axis direction. In this way, the force to prevent the movement of the movable body can be intensified. Therefore, when the movable body is halted in a predetermined position, the force to move the movable body and the force to prevent the movement of the movable body both intensify so that the movable body can be halted in the position with more stability. For example, even when a cell phone is swung around and another kind of force such as a centrifugal force is exerted in the lens optical axis direction, the movable body can be halted with stability. By using two resilient members to compose the resilient member, the bad effect of another force such as a centrifugal force is relatively reduced; therefore, the above mentioned linearity can be further improved. Note that, by using two resilient members, the resilient members are kept from deterioration over the time, compared to using a single resilient member.
In at least an embodiment of the present invention, it is preferred that the first and second resilient members be metallic resilient members that electrify the coil. According to at least an embodiment of the present invention, the metallic resilient members that electrify the coil are used for the first and second resilient members; therefore, the first and second resilient members can be used as a wire for electrifying the coil. In this manner, the design of an electrical circuit (circuit wiring) of the lens driving apparatus can be simplified, contributing to downsizing the lens driving apparatus overall.
In at least an embodiment of the present invention, the coil is arranged to be opposed to the magnet in the lens optical axis direction.
In this case, it is preferred that the coil be arranged in multiple so that the magnet is interposed between the coils in the lens optical axis direction. According to at least an embodiment of the present invention, the coil is arranged in multiple (two coils, for example) so that the magnet is interposed between the coils in the lens optical axis direction; therefore, the magnetic flux emanated from the magnet in one direction in the lens optical axis direction and the magnetic flux emanated from the magnet in the opposite direction in the lens optical axis direction can be converted to an electromagnetic force by the multiple coils. Therefore, a thrust force can be effectively produced in the movable body, which in turn efficiently halts the movable body in the desired position.
In at least an embodiment of the present invention, when the coil is arranged to be opposed to the magnet in the lens optical axis direction, the magnet may be arranged in multiple so that the coil is interposed between the magnets in the lens optical axis direction. According to at least an embodiment of the present invention, the above mentioned magnet is arranged in multiple (two magnets, for example) so that the coil is interposed between the magnets in the coil can be intensified, compared to a method using a single magnet and the lens optical axis direction; therefore, the density of the magnetic flux around multiple coils is intensified; even if the number of coils to produce a thrust force is reduced to one, a thrust force at the same level can be produced, and the form of the magnetic circuit can be flat. Thus, the lens driving apparatus can be made thinner or smaller; in addition, the movable body can be halted in the desired position. Also, when only one coil is interposed between the magnets, a connecting wire between the coils is not necessary, thus improving operability.
In at least an embodiment of the present invention, when the coil is arranged to be opposed to the magnet in the lens optical axis direction, the magnet may be arranged singly to be opposed to the coil in the lens optical axis direction. According to at least an embodiment of the present invention, the above mentioned magnet is arranged singly to be opposed to the coil in the lens optical axis direction; therefore, only one coil is opposed to the magnet, that is, a combination of one magnet and one coil may be used to make a thinner or smaller lens driving apparatus.
In at least an embodiment of the present invention, it is preferred that the lens driving apparatus further comprise a yoke that changes the direction of the magnetic flux emanated from the magnet, the yoke be formed such that its length in the lens optical axis is longer than at least the opposing surface-to-surface distance between the coil(s) and/or the magnet(s), and also arranged in the movable body and/or said fixed body. According to at least an embodiment of the present invention, a yoke having the length in the lens optical axis direction longer than at least the opposing surface-to-surface distance between the coil(s) and/or the magnet(s) is arranged to either movable body or the fixed body or to both bodies (when two coils are used, it is the distance between the opposing surfaces of the coils in the optical axis direction; when two magnets are used, it is the distance between the opposing surfaces of the magnets in the optical axis direction; when one coil and one magnet are used, it is the distance between the opposing surfaces of the coil and the magnet in the optical axis direction); therefore, magnetic flux leaking from the magnetic path between the magnet and coil can be reduced, which in turn further improves the linearity between the moving distance of the movable body and the current flowing in the coil.
In this case, it is preferred that the magnet and the yoke be held in the other body (either the movable body or the fixed body, whichever holds the magnet). According to at least an embodiment of the present invention, the above mentioned magnet and yoke are both arranged in one of the bodies; therefore, the relative positional relationship between the magnet and the yoke is constant, and so the bad effect caused by an attraction force between the magnet and the yoke can be prevented. In other words, since the yoke is a magnetic material, the yoke is magnetized when the magnet is near, and then a magnetic attraction force exists between the two members in the radial direction. If the relative positional relationship between the magnet and the yoke is changed under such a condition, when the movable body on which the magnet is arranged is moved in the optical axis direction with respect to the fixed body to which the yoke is arranged, for example, the lens driving apparatus is badly affected by the attraction force. Also, if the magnet and the yoke are both arranged in the movable body or in the fixed body as in at least an embodiment of the present invention, both members move together or neither member moves; therefore, the relative positional relationship between the members can be constant, thus preventing the bad effect which may be caused by a magnetic attraction force between the magnet and the yoke.
In at least an embodiment of the present invention, it is preferred that the drive mechanism be equipped with a magnetic member which is held in the body and is magnetically attracted to the magnet. With this configuration, a magnetic attraction force exists between the magnetic member and the magnet. Therefore, while an electromagnetic force of the coil and a regulating force of the regulatory means attain equilibrium so that the movable body can be halted in an appropriate position for macro photography, the magnetic attraction between the magnetic member and the magnet can be used to retain the movable body for a normal snapshot (or when a camera is not in use). In particular, in at least an embodiment of the present invention, the movable body is retained not by the urging force of a spring, but by a highly stable magnetic attraction force, unlike the above mentioned conventional lens driving apparatus. Therefore, inaccuracy of the static position of the movable body can be prevented and the accuracy will be more stable. Note that the manufacturing of a spring that retains the movable body is not necessary, thus contributing to reduced cost in manufacturing. Also, the “magnetic member” in at least an embodiment of the present invention can be any substance as long as a magnetic attraction force can be created with the magnet to some extent. For example, even if a member is generally known for non-magnetic characteristics, it would be “a magnetic member” if it generates even a small force of magnetic attraction with the magnet. Also, the “magnetic member” can be of any form, type, and size.
In at least an embodiment of the present invention, it is preferred that the magnetic member be formed in a circular shape and arranged coaxially with the lens optical axis. According to at least an embodiment of the present invention, the above mentioned magnetic member is formed in a circular shape and arranged coaxially with the lens optical axis; therefore, a magnetic attraction force can be produced with the magnet with better stability, and the accuracy in the static position of the movable body can be more stabilized. In other words, when small pieces of the magnetic member are equidistantly arranged along the coil in the circumferential direction, a magnetic attraction between the coil and the magnet can be uneven depending on the distance between the pieces, and the accurate static position of the movable body cannot be obtained with stability. However, according to at least an embodiment of the present invention, a magnetic member formed in a circular shape is arranged coaxially with the lens optical axis; therefore, an uneven magnetic attraction force with the magnet will not be caused but an even magnetic attraction force is produced anywhere around the coil in the circumferential direction. This stabilizes accuracy in the static position of the movable body even more.
In at least an embodiment of the present invention, the above mentioned magnetic member may be in the form of a ball, wire or bar. In this case, it is preferred that the magnetic member be adjustable in the number to be mounted and in size. With this configuration, the number of the magnets to be mounted and the size are so optimized that the inclination of the movable body can be corrected.
In at least an embodiment of the present invention, it is preferred that the magnet be held in the fixed body, and the magnetic member be held in the movable body at a position at which the magnetic member is closer to the photographic subject than the magnet is. According to at least an embodiment of the present invention, the magnetic member is closer to the photographic subject than the magnet is; therefore, the movable body is attracted in the opposite direction from the direction it moves when used for macro photography. For this reason, the movable body can be retained by a magnetic attraction force produced between the magnetic member and the magnet during a normal snapshot (or when the camera is not in use), providing a more stable accuracy in the static position of the movable body.
In at least an embodiment of the present invention, the resilient member may be composed of a member that is to be magnetically attracted to the magnet. In this case, the resilient member used as a regulating member produces a magnetic attraction with the magnet. Therefore, the movable body can be retained not by using the urging force of the spring but by using a highly stable magnetic attraction. This prevents inaccuracy of the static position of the movable body, stabilizing the accuracy in the static position of the movable body.
In at least an embodiment of the present invention, when the first resilient member and the second resilient member are used as the regulatory means, either the first resilient member or the second resilient member is composed of a member that is to be magnetically attracted to the magnet. With this configuration, a magnetic attraction is caused between the first resilient member and the magnet, for example. Therefore, either the first resilient member or the second resilient member which is on the photographic subject side (for example, the first resilient member) is attracted to the magnet so that the movable body can be retained by using a highly stable magnetic attraction during a normal snapshot (or when the camera is not in use), thus stabilizing accuracy in the static position of the movable body.
In at least an embodiment of the present invention, the coil is held on the outer circumference of the movable body.
In this case, it is preferred that the coil be directly wound around the movable body. With this configuration, the space occupied by the coil can be reduced, compared to the configuration using a bobbin. Also, when the space occupied by the coil is kept as it is, the number of windings of the coil can be increased.
In at least an embodiment of the present invention, when the coil is held on the outer periphery of the movable body, it is preferred that the fixed body have a cover portion that surrounds the movable body and the magnet, and the magnet be arranged along the inner periphery of the cover portion. According to at least an embodiment of the present invention, the magnet is shaped along the inner periphery of the cover portion; therefore, the space between the inner peripheral surface of the cover portion and the outer circumferential surface of the coil can be utilized as a space for positioning the magnet, thus reducing dead space. Also, since the magnet can be efficiently filled between the inner peripheral surface of the cover portion and the outer circumferential surface of the coil, a magnet of a larger mass can be used, which helps produce a magnetic field that is interlinked with the coil efficiently.
In at least an embodiment of the present invention, the cover portion in a non-circular inner peripheral shape surrounds the movable body and the magnet.
In at least an embodiment of the present invention, it is preferred that the inner peripheral shape of the cover portion and the outer circumferential shape of the coil be different from each other when viewed in the optical axis direction.
In at least an embodiment of the present invention, it is preferred that the plane shape of the regulatory means agree with the plane shape of the cover portion.
In at least an embodiment of the present invention, it is preferred that multiple magnets be equidistantly arranged in multiple positions in the circumferential direction. With this configuration, the magnets can be efficiently filled in the space between the inner peripheral surface of the cover portion and the outer circumferential surface of the coil; therefore, a magnet of a large mass can be used, which in turn helps produce efficiently a magnetic field which is interlinked with the coil.
In at least an embodiment of the present invention, it is preferred that the coil be wound annularly, and when the inner peripheral shape of the cover portion is polygonal, the magnet be arranged at a position which includes at least one of the multiple corners in the inner peripheral shape of the cover portion.
In at least an embodiment of the present invention, it is preferred that the coil be wound annularly, and when the inner circumferential shape of the cover portion is square or polygonal in which the corner portions of square are chamfered, the magnets be arranged in the corner portions of the square.
In at least an embodiment of the present invention, it is preferred that the magnet be positioned with the corner portion of the cover portion. With this configuration, there is no need to provide a jig for positioning the magnet at the cover portion, increasing efficiency in operation.
In at least an embodiment of the present invention, it is preferred that the cover portion be a tube-like body portion of a back yoke, and the magnet is adhered on the inner peripheral surface of the tube-like body portion of the back yoke.
In at least an embodiment of the present invention, it is preferred that the fixed body is composed of a base, which is placed on the tube-like body portion of the back yoke on the image pickup device side in the optical axis direction, and a case, which is placed on the tube-like body portion of the back yoke on the photographic subject side and the back yoke, the base, and the case have the identical outer peripheral shape when viewed from the optical axis direction.
In at least an embodiment of the present invention, it is preferred that the back yoke have an inner yoke which extends from the tube-like body portion to the inner side of the coil. With this configuration, the density of a magnetic flux that is interlinked with the coil can be intensified.
In at least an embodiment of the present invention, it is preferred that a coil yoke be arranged on the other side of the coil from the side on which said magnet is arranged. With this configuration, the density of a magnetic flux that is interlinked with the coil can be intensified.
In at least an embodiment of the present invention, the magnet can be positioned on the outer circumference side of the coil and can also be positioned on one side of the coil in the optical axis direction. However, it is preferred that the magnet be positioned on the outer circumference side of the coil from the view point of making a thinner lens driving apparatus.
In this case, it is preferred that the magnet be arranged such that the inner face thereof extends along the outer circumference of the coil.
In at least an embodiment of the present invention, when the magnet is positioned on the outer circumference side of the coil, the magnet may be magnetized to unlike poles in the inside-outside direction.
In at least an embodiment of the present invention, the magnet may be composed of two magnet pieces, each of which is magnetized to unlike poles in the optical axis direction, and the two magnet pieces may be layered in the optical axis direction such that like poles make contact with each other. With this configuration, magnetic lines of force are intensely produced in the vicinity of the layered portion of the two magnet pieces; therefore, a magnetic field that is interlinked with the coil can be efficiently produced.
In at least an embodiment of the present invention, it is preferred that the magnet be composed of multiple magnet pieces which are layered in the optical axis direction, the coil be arranged in multiple in the optical axis direction to be opposed to each of the multiple magnetic pieces, and each of the multiple magnet pieces be magnetized to unlike poles in the inside-outside direction and the magnetizing directions in the magnetic pieces, which are adjacent to each other in the optical axis direction, be opposite from one another in the inside-outside direction. With this configuration, the density of the magnetic flux that is interlinked with the coil can be intensified.
In at least an embodiment of the present invention, it is preferred that the magnet have a plurality of divided magnetized areas along the optical axis direction, the coil be arranged in multiple in the optical axis direction to be opposed to each of the plurality of divided magnetized areas, each of the plurality of divided magnetized areas be magnetized to unlike poles in the inside-outside direction, and the magnetizing directions in the magnetized areas, which are adjacent to each other in the optical axis direction, be opposite from one another in the inside-outside direction. With this configuration, the density of the magnetic flux that is interlinked with the coil can be intensified.
In at least an embodiment of the present invention, it is preferred that the fixed body have a plate-like cover that is placed on the case on the photographic subject side. With this configuration, foreign matter such as particles are prevented from coming into the lens driving apparatus.
In at least an embodiment of the present invention, it is preferred that the plate-like cover have engaging leg portions which are to be engaged with the other member configuring the fixed body.